Cooling systems are already known, for example from EP 0 664 424 A2, in which a method for lubricating bearings in refrigerant compressors is to be improved. To this end, a small amount of a refrigerant/oil mixture is introduced into the vicinity of a bearing, wherein the refrigerant is vaporized due to the bearing temperature and a lubricant including at least 75 volume percent of oil is deposited onto the bearing. Only thereby it is ensured that a sufficiently thick lubrication film is provided in the rolling contact for avoiding boundary layer lubrication with an immediate contact of the bearing components in the rolling contact. Thereby, the flow path of the refrigerant and the configuration of the bearing need to be designed such that a sufficient volume of refrigerant with at least 75% oil is deposited in all circumstances. In particular, if the refrigerant compressor has not yet reached its operating temperature, the bearing environment needs to be able to vaporize a sufficient amount of refrigerant from the refrigerant oil mixture.
Further, from EP 1 729 055 B1, lubrication systems for rolling elements in refrigerant compressors are known, in which the lubrication medium consists of an ultra-low viscous volatile fluid (ULVVF). For lubricating and guaranteeing a sufficiently thick liquid lubrication film, it is proposed to inject the liquefied fluid and to keep the fluid at least partly above the evaporating pressure by using a flow restriction. The disadvantage in this case is that, even if it has been ensured that the fluid for lubricating the rolling elements forms a liquid lubrication film and the bearing does not run dry, the bearing has to withstand extreme demands due to the poor lubrication characteristic of the fluid, which does not include lubrication oil, and therefore only high resistant and thus expensive bearings may be used in this application area.
Further, rolling element bearings are already known from EP 0 711 929 B1, in which at least one rolling element consists of a material which is harder or more rigid than the steel material of the other rolling elements, which results in a greater hardness of the at least one rolling element with respect to the other rolling elements.